In a graphics display device, such as an LCD (Liquid Crystal Display) panel, data for display as well as instructions for displaying the data are provided by a host. In principle, any host can interface directly with a display device provided that the host's read/write operations conform to the protocol specified for the display device. However, it is often desirable to provide an application specific graphics controller as a separate chip, such as an LCD controller, between the host and the display device to provide specialized functions. For example, an LCD controller chip might be used to automate the transfer of images from a camera to an LCD panel, or to allow a host having a parallel bus to interface with an LCD panel having a serial interface and vice versa.
A specific example of such an LCD controller is used in a cellular telephone. The telephone includes a microprocessor functioning as a host CPU, a camera, and may include three LCD panels which, for purposes herein, may be considered elements of a single graphics display device. The LCD controller provides a camera interface for receiving video data from the camera, converting the video data into a displayable form, and transmitting the data. The LCD controller is also provided with a JPEG encoder/decoder (“CODEC”) for encoding outgoing video data for transmission and decoding incoming video data for display. The LCD controller further provides other functions, such as cropping or otherwise resizing the image to eliminate selected data, and translating the data from one color space to another. In telephone and other systems used for data communications, such controllers are used for both wireless and wired communications.
In the example given above, the host generally also provides video data to the LCD panels for display, and the host issues commands to the LCD panels, to enable the selected LCD panel(s), and to specify display parameters, such as image size and color resolution. The host may also read data from the LCD panels. For example, the host may read status bits in the LCD panels, or may read images taken by the camera from the LCD panels, e.g., to resize the images.
Where an application specific graphics controller is provided, the host communicates through the controller rather than directly with the graphical display device. Data would otherwise move between the host and the graphics display device without the processing provided by the graphics controller. Accordingly, the graphics controller is provided with the capability to receive data written to the graphics controller by the host in a memory, and to read out from the memory the data received from the host to the graphics display device. However, it is recognized herein that the controller nevertheless adds delay in such transmissions. Accordingly, there is a need for a graphics controller providing flexible access to a graphics display device by a host that minimizes or eliminates this delay.